1. Field of the Invention
The subject invention is generally related to a centrifuge vessel which is rotated at high speed about its longitudinal axis and, more particularly, to a centrifuge vessel which can be used to separate an analyte from a biological solution in an automated fashion.
2. Description of the Prior Art
Centrifuges are well known commercial and laboratory tools that are used to separate materials of varying densities. Centrifuges are often used for clarifying liquids whereby suspended solids such as cells or proteins are sedimented from solution by high speed rotation of the centrifuge vessel. Two common types of centrifuges are the horizontal centrifuge and the fixed angle centrifuge.
In the conventional horizontal centrifuge, sample containers of the solution to be centrifuged are placed in holders called "buckets". These buckets are subsequently attached to a vertical rotor in a balanced arrangement and swung to a horizontal plane under centrifugal force. While being rotated at high speeds in the horizontal position, the denser particles in the sample move along an unimpeded path toward the bottom of the buckets to form a smooth, even "pellet" of sedimented material. The non-pelleted supernatant solution can be decanted from the bucket once centrifugation is halted.
In the conventional fixed angle centrifuge, a rotor holds a plurality of sample containers at fixed angles relative to the axis of rotation. In the same fashion as in the horizontal centrifuge, at least a pair of sample containers must be used in order to balance the rotor during high speed spinning. During high speed rotation of the fixed angle rotor, the denser particles in the sample containers pellet along the side wall of the container. Pelleting on the side wall does make decanting of the supernatant more difficult because of the possible resuspension of the pellet; however, there are certain advantages in using the fixed angle centrifuge. For example, in the fixed angle centrifuge there is a shorter path for sedimentation resulting in a shorter time for separation and, more importantly, higher speeds of rotation are achievable with fixed angle rotors because they are subjected to less air turbulence than the hanging bucket centrifuges. Higher rotation speeds allow greater centrifugal forces to act on the suspended solids.
As pointed out above, in both the horizontal and the fixed angle centrifuges, the rotor must be balanced accurately in order to prevent damage to the centrifuge. In order to properly balance the rotor, the lab technician must precisely weigh each centrifuge sample container using a balance and then position two sample containers of equal weight in the rotor on opposite sides. This balancing step is very tedious and often requires withdrawing and adding back sample to the sample container until it reaches the desired weight.
In U.S. Pat. No. 4,639,242 to Babson, the complete disclosure of which is incorporated herein by reference, a vessel was described which allowed for the complete physical separation of a precipitate and supernatant in a single tube. In operation, a precipitating agent is first mixed with the biological specimen and given time to react with analyte therein. Then the tube is rotated about its longitudinal axis at high speed. During high speed rotation, the contents of the tube is forced against the inner wall of the tube and moves upward towards the top of the tube due to the tube's inclined inner surface. At the top of the tube, the precipitate is deposited within V-shaped grooves on the tube's interior. After rotation is stopped, the precipitate is retained in the V-shaped grooves at the top of the tube while the liquid drops back to the bottom of the tube.
U.S. Pat. No. 4,639,242 to Babson also discloses a procedure for using the tube whereby a radioactively labelled antibody is bound in the bottom of the tube. The radioactively labelled antibody reacts with an analyte of interest in the biological fluid during a short incubation time during which the biological fluid is permitted to mingle with the bound antibody so that it may bind the analyte of interest. Then the tube is rotated at high speed, thereby causing the fluid in the tube to rise to the top while the analyte remains bound to the antibody in the bottom of the tube. The radioactivity in the bottom of the tube is counted while the tube is spinning.
While the tube disclosed in U.S. Pat. No. 4,639,242 to Babson is more adaptable to an automated processing environment than conventional horizontal and fixed angle centrifuges because it does not require the batch step of balancing pairs of rotor tubes, the Babson tube is not suitable for some of today's processing environments. For example, in some environments it may not be desirable to have a precipitation step. Not only does precipitation require extra chemicals to be used and time for the precipitation reaction to take place, but in some environments precipitation may reduce yield or the precipitating agent itself may affect the measured results. In addition, it may be desirable to stop the tube from spinning and use other instrumentation to make radioactive, fluorescent, or other related readings.